1. Field of the Invention
The present invention pertains to an insert boring tool such as an end mill and a drill bit, and to a cutting insert suitably utilized for such a boring tool.
2. Prior Art
FIGS. 1 and 2 of the acompanying drawings show an example of a conventional insert end mill which comprises a generally cylindrical tool body 100 having an axis O of rotation therethrough and having a pair of chip pockets 102 formed in a forward end portion 104 thereof. An insert receiving recess or seat 106, 108 is formed in a wall surface of each chip pocket 102 facing in the direction of rotation of the body 100, the recess 106 being disposed adjacent to the axis O of the body 100 while the recess 108 is spaced radially outwardly from the axis O of the body 100. A pair of cutting inserts 110, each of which comprises a generally rhombic plate having a pair of diagonally opposed acute corners, are releasably received in the recesses 106 and 108, respectively, and fixedly secured thereto through clamp screws 112, respectively.
Each insert 110 has a front surface 114 having marginal ridges serving as cutting edges and a rear surface 116 to be rested on a respective one of the recesses 106 and 108. The insert received in the recess 106 is disposed so that one of the cutting edges is indexed in an end cutting position to serve as an end cutting edge 118 while the insert received in the recess 108 is disposed so that in addition to one of the cutting edges indexed in an end cutting position to serve as an end cutting edge 120, the cutting edge which intersects the indexed end cutting edge 120 at an acute angle is indexed in a peripheral cutting position to serve as a peripheral cutting edge 122.
Thus, when the end mill is rotated about the axis O of the body 100 to form a groove G in a workpiece W, the end cutting edges 118 and 120 of both the inserts 110, as schematically shown in FIG. 3, cooperate to cut the workpiece to form a bottom G.sub.1 of the groove while the peripheral cutting edge 122 of the insert 110 received in the recess 108 forms inner peripheral surface G.sub.2 of the groove.
In the end mill as described above, however, the inserts 110 are liable to undergo a great thrust load particularly upon beginning to engage the workpiece, and besides the cutting speed is relatively low at the radially inner ends of the respective end cutting edges, designated at 118a and 120a in FIG. 3. Therefore, such inner ends of the end cutting edges 118 and 120 have been susceptible to chipping or fracture.